[MRUNIT-127] Key grouping with GroupingComparators is not consistent with MapReduce behaviour

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 0.9.0
• Fix Version/s: 1.0.0
• Assignee: Dave Beech
• Reporter: Dave Beech
• Created: 31/Jul/12 21:19
• Updated: 03/Aug/12 09:41
• Resolved: 03/Aug/12 09:41

Description

In Hadoop MapReduce, for a set of keys to be properly grouped together by a grouping comparator into a reduce call, they need to be in a contiguous range when sorted by the key's ordering comparator.

MRUnit does not impose this requirement, so if the user's grouping and sorting comparator logic is incorrect, their tests may pass and give the expected result even though the outcome would be different when run as a true MapReduce job.

(see below for further explanation)